The present invention relates to sliding homokinetic joints employed in particular for the transmission between a motor-drive unit and the front driving wheels of a front-drive vehicle.
In such vehicles, it is known that the transmission shaft must allow the relative movement between the wheels and the suspended part of the vehicle and must therefore be able to absorb an angular alignment defect and modifications of the distance between the motor-drive unit and the wheels during the transmission of the torque. This application and other applications therefore require a wide angle of breaking of the joints and a sliding capacity. A first arrangement employs an axially fixed joint having a large breaking capacity or a large angularity, the sliding being then ensured separately by a splined connection. The angular movement and sliding functions are theoretically possible, but it may be observed that the splines slide with difficulty under torque and that the axial reactions transmitted to the motor and to the bearing of the wheels result in various drawbacks such as: the transmission of vibrations of the motor to the wheel hub and to the structure or the body of the vehicle; fatigue in the bearings of the wheel hub and of the output member of the differential; a relatively high cost due to the fact that each one of the two functions is ensured by separate means.
A second arrangement employs a sliding homokinetic joint of the tripod type which performs on the whole very well and simultaneously, the two functions of transmission of torque at an angle and sliding. The devices of this type, described for example in French Patent No. 1,272,530 filed July 4, 1960 by the Applicant, usually comprise a first element or tripod integral with one of the shafts to be coupled and carrying two rollers, and a second element or bell integral with the other shaft to be coupled and having the general shape of a cylindrical ring in which there are formed three raceways which have a circular cross section and in which the rollers carried by the tripod are received. It has been observed that when such a joint operates at an angle, the axis of the shaft integral with the tripod effects, upon rotation, a planetary movement around a mean position so that the maximum breaking angle-which corresponds to a limit position for which one of the rollers is at the end of its raceway, whereas the tripod shaft comes roughly in contact with the free inner edge of the bell-is determined by the most unfavourable position of the shaft integral with the tripod with respect to said bell, corresponding to one of the two extreme positions of the shaft in the course of its planetary movement. As the usual shape of the inner wall of the bell is that of a bore of circular section, it will be understood that the maximum break angle is less, everything else being equal, than the maximum break angle that would be possible with a homokinetic joint in which the shaft integral with the tripod does not undergo a planetary movement.